This invention relates to fluid nozzles and, more particularly, to fluid nozzles of the spill-back or by-pass type.
The discharge quantity from liquid nozzles has been regulated or modulated for many years by by-passing or spilling back a portion of the fluid introduced to the nozzle. Such nozzles have been variously known as by-pass nozzles, return flow nozzles, recirculating nozzles, spill or spill-back type nozzles and, sometimes, Peabody-Fisher nozzles after the name of the original developers of the nozzle. By-pass nozzles have found wide spread use in the combustion field as fuel nozzles, since the spray discharge from the nozzles may be easily regulated over wide ranges and regulation is simple, inexpensive, and necessitates only a minimum of mechanical parts.
In by-pass nozzles, the liquid is injected into a chamber through one or more inlet orifices which usually enter the chamber tangentially or at an angle to the chamber axis so as to induce a swirling or vortexing of liquid in the chamber. This swirling liquid is then discharged from the chamber in the form of a hollow spray cone through the discharge orifice of the nozzle. In order to regulate or modulate the quantity of flow through the discharge orifice, a by-pass orifice also communicates with the chamber. When the conduit leading from the by-pass orifice is closed, such as by the shutting of a by-pass valve in the conduit, all of the liquid introduced through the inlet orifices into the chamber will be discharged through the discharge orifice in the form of the spray cone. When it is desired to selectively reduce the amount of liquid being discharged so as to modulate the discharge, the by-pass valve is selectively opened so as to by-pass or spill-back some of the liquid introduced into the chamber back to the liquid supply or low pressure side of the system. The amount of liquid exiting through the discharge orifice, therefore, will vary, depending on the amount of liquid which is spilled back through the by-pass conduit.
One of the terms frequently used in the by-pass nozzle art is "turndown ratio". The turndown ratio is a measure of the modulation performance characteristics of the nozzle. More specifically, the turndown ratio is the ratio of the maximum flow from the discharge orifice (for example, when the by-pass is closed) to the flow that exists under any particular set of given operating conditions. For example, if a nozzle's ultimate capability might be a ratio of 50:1 (by-pass fully closed to fully opened), it may at any particular time be operating at a lower turndown ratio of say 4:1 when the by-pass is only partially opened. Therefore, the turndown ratio is a function, at any given time, of the amount of liquid which is spilled back through the by-pass conduit.
One of the major problems arising in prior art by-pass nozzles is that the total flow through the inlet orifices will increase substantially as the amount of liquid being by-passed increases, i.e., as the turndown ratio is increased. This phenomenon is commonly known in the by-pass nozzle art as "total flow growth". Prior art by-pass nozzles commonly experience total flow growths of 30-50% or more at turndown ratios of 3:1. In other words, the total flow through the inlet orifices is 30-50% greater in these nozzles at a 3:1 turndown ratio than when the by-pass is fully closed. Thus, while the quantity of sprayed liquid is being reduced by opening the by-pass valve, the total quantity of liquid which must be supplied to the nozzle, assuming constant pressure to the nozzle, is increasing.
This total flow growth is objectionable for several reasons. One reason is that further increases in the input horsepower requirements of the nozzle are necessary. Some increase in horsepower is inherent in all by-pass nozzles due to the fact that some input energy is always lost because some of the pressurized liquid is simply returned to the low pressure side of the system. Where total flow growth is high, the amount of this wasted energy is high.
An even more significant disadvantage of high total flow growth is that the input pump must be substantially over-designed in capacity so that the measurable increase in total flow can be accomplished over the entire range of operation. Moreover, if the input flow is held constant, such as where the supply pump is a constant displacement pump, instead of allowed to rise, there will be a decrease in the overall nozzle pressure, which could, in turn, degrade spray quality and aggravate variations in spray cone angle.
Some attempts have been made to reduce this undesirable total flow growth. Graham et al, U.S. Pat. No. 1,824,952, attempted to reduce total flow growth by locating a diaphragm valve in the high pressure input conduit to regulate the pressure in response to variations in pressure in the by-pass return conduit. And, in Olches, U.S. Pat. No. 2,290,350, an elaborate system of valves and check valves is disclosed for minimizing total flow growth. Both of these systems are less efficient than the present invention and are considerably more elaborate because they necessitate the provision of additional valves and the like.
It is a principal purpose of the present invention to substantially reduce the total flow growth as liquid is by-passed in a by-pass nozzle. It has been found when practicing the principles of the present invention that modest total flow growth, on the order of less than 15%, may be realized for turndown ratios of 3:1, as compared to total flow growths which are typically 30 to 50% in the prior art nozzles for the same turndown ratio. Since the nozzles incorporating the principles of the present invention substantially reduce total flow growth, the need for complex valve and other control arrangements is minimized, as is the need for excessive pump capacities and energy losses which otherwise accompany large total flow growths. Moreover, in the nozzle incorporating the principles of the invention, variations in the spray angle over wide turndown ratios are minimized and the effects of by-pass flow resistance changes are minimized. The nozzle constructed in accordance with the principles of the invention is capable of virtually infinite turndown ratios and may be easily disassembled and employ interchangeable metering parts.
In the present invention, a fluid by-pass nozzle includes a chamber, inlet orifice means for introducing fluid to the chamber, discharge orifice means for discharging fluid from the chamber, and by-pass means for selectively removing a predetermined portion of the fluid introduced by the inlet orifice means to the chamber to regulate the quantity of fluid discharged from the discharge orifice means. The improvement in such nozzle is that the ratio of the total cross-sectional area of the inlet orifice means to the cross-sectional area of the discharge orifice means is less than 1.50.
These and other objects, features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.